I know Greg has said that belts should be used when hitting 95% or more of your 1RM. Not sure about the knee sleeves though. I know there are a couple of topics on the subject around here. I know Oly has specific rules when it comes to knee sleeves in competition, they can't touch the bottom of your singlet (I'm not sure why this is a rule).
I've used belts on occasion and probably should use them more often but I don't currently own one but am eyeing one that Dave recommended over a few months ago.
"And for crying out loud. Don't go into the pain cave. I can't stress this enough. Your Totem Animal won't be in there to help you. You'll be on your own. The Pain Cave is for cowards.
Pain is your companion, don't go hide from it."